1. Field of Application
The present invention relates to a control apparatus for an electrical generator of a vehicle, which monitors the generating status of the generator, and controls functions such as turning on the generator warning lamp (i.e., charging lamp) of the vehicle, etc.
2. Description of Prior Art
In the prior art, types of control apparatus for an electrical generator of a vehicle are known for a vehicle which is equipped with a charging lamp that serves to notify the vehicle driver of any abnormal operation of the generator, whereby the control apparatus has a short-circuit protection function which prevents destruction of a charging lamp drive transistor when a short-circuit occurs in the charging lamp, by preventing an excessively high level of current flow. For example as described in U.S. Pat. No. 4,812,723 “Control Device for an A.C. Generator for an Automobile”, a current level which is set as a threshold value for detection of the short-circuit condition of a charging lamp is made lower than a peak initial value of surge current which flows through the charging lamp when power is applied to the lamp with the lamp in a cold condition (and hence initially having a low value of resistance). When the current flow in the charging lamp exceeds that detection value, because the charging lamp is in the short-circuit condition or because the lamp is in a normal condition but an initial high surge of current through the lamp is occurring, the transistor which supplies the charging lamp with current is repetitively switched between the on and off states. This allows the effective value of current flow through the charging lamp to be limited such as to prevent damage to the transistor which drives the charging lamp, i.e., with only brief repetitive large values of current flowing through that transistor, so that overheating of the transistor does not occur. In that condition, if the charging lamp is not in the short-circuit state, it will become gradually heated. As a result, its resistance will increase, and the current flow through the lamp will decrease accordingly. When that value of current falls below the detection value, the repetitive on/off switching operation is halted, and current is allowed to pass continuously through the lamp, i.e., the normal steady-state level of current.
However while the repetitive on/off switching operation is being performed, the charging lamp may appear to the driver to be emitting light only very dimly, or not at all. If the charging lamp is in the short-circuit condition, then the repetitive on/off switching operation will continue until the lamp is replaced.
Another example of such a control apparatus for an electrical generator of a vehicle is described in Japanese patent 60-66631 “Charging Display Apparatus for Electrical Generator of Vehicle”, and Japanese patent 6-189467 “Voltage Control Apparatus for AC Generator of Vehicle”.
Normally, when the driver of a vehicle turns on the ignition switch, before actually starting the vehicle engine, the charging lamp will light, to indicate that the generator is not yet in operation, i.e., no charging current is being supplied to the battery. With such prior art types of control apparatus, particularly if the vehicle is being operated in a cold environment, some time may elapse after the ignition switch is turned on and the aforementioned repetitive on/off switching supply of current to the charging lamp begins, until the charging lamp becomes sufficiently warm that the control apparatus begins to drive the lamp with a continuous flow of current. Thus there will be a period of delay after the ignition switch is turned on, before the charging lamp begins to emit the normal level of light. This can cause uneasiness to the driver, who may for example mistakenly believe that there is a problem with the electrical system of the vehicle.
If it is attempted to overcome this by increasing the threshold value that is used to detect the short-circuit current level, then another problem arises. Specifically, a short-circuit condition of the charging lamp may not be a perfect short-circuit, but may result in a level of resistance which is intermediate between the normal value and the short-circuit value, and if the above measure of increasing the detection threshold value is adopted, then it may become impossible to detect such a partial short-circuit condition. Furthermore, large values of current flow may occur through the charging lamp drive transistor, which may result in overheating and destruction of that transistor, or overheating and melting of the connecting leads which supply current to the charging lamp.
It can thus be understood that in the prior art, it has not been possible to provide a control apparatus for an electrical generator of a vehicle whereby certain basic conditions can both be satisfied, i.e.:
(a) the capability for distinguishing between a high level of current flow through a display device drive transistor that results from a temporary surge of current through a display device which is functioning normally, and a high level of current flow that results from a short-circuit condition,
(b) the capability for reliably detecting both a complete short-circuit and a partial short-circuit condition of the charging lamp (i.e., whereby there would be a level of current flow through the charging lamp that is lower than the level which would occur in the case of a complete short-circuit, but is higher than a normal steady-state level of current flow through the charging lamp) and
(c) the capability for driving the charging lamp to provide an immediate indication that the vehicle generator is not functioning, when such a condition is detected.